Shell Scripting to Read Data From a File

Okay, so here's your problem: you have a file that contains data that you'd like to parse through a script. It's a lot of data and you don't want to sit there and continuously do the same thing over and over!

The data can be set up as one long column of data or multiple columns of data. In this case for simplicity I'll only use one column of data.

So let's say your data file is as follows:

dog
cat
cow
...
...
(long list of data)


These represent parts of filenames that you need to clear out. You don't want to sit there typing cat /dev/null > dog
cat /dev/null > cat
... So you come up with a master plan to script the process. The script will be short, sweet, and absolutely time saving!

You first need to read in the file; so this line does the work for you: exec < files.txt. Obviously, in this example my "files.txt" is the filename that contains the data I want to read. After you've opened up the file for reading, you can now parse through the file with a while loop:
while read file ; do
[do some work here]
done


Now note, "file" is the variable that we're assigning to the column. You can call the variable whatever you want. Also remember that I am being simple with this example and only have one column of data. If I wanted to do multiple columns of data, I would just assign more variables to each column. e.g. while read col01 col02 col03 ; do where $col01, $col02, and $col03 will be my new variables.

That's it! I'll leave the customization to you. Cheers!

Here is the full script example:
#!/usr/bin/bash

exec < files.txt

while read file ; do
if [ -s /mnt/$file ] ; then
cat /dev/null > /mnt/www/vdir/z/ec/$file
else
echo "/mnt/$file already empty!"
fi
done